In the related art, a hot-water storage type heating unit is known which includes a hot-water storage tank which stores hot water in the inner portion, a hot-water circulation circuit through which the hot water stored in the hot-water storage tank circulates, a radiation circuit to which a radiator is connected and through which a heating medium flows, a liquid-liquid heat exchanger which exchanges heat between the hot water which circulates through the hot-water circulation circuit and the heating medium which flows through the radiation circuit, and a pump which is disposed in the hot-water circulation circuit on the downstream side of the liquid-liquid heat exchanger and circulates the hot water in the hot-water circulation circuit.
For example, Patent Document 1 discloses that hot water in a hot-water storage tank is heated by a heat pump, heat is exchanged between the heated hot water and water supplied from a water supply pipe by a liquid-liquid heat exchanger, and the hot water is supplied. Since the hot water with a high temperature is stored in the upper portion of the hot-water storage tank, the hot water is sucked from the upper portion of the hot-water storage tank and is supplied to the liquid-liquid heat exchanger.
In this configuration, if the liquid-liquid heat exchanger is disposed above the hot-water storage tank, air stays in the liquid-liquid heat exchanger, the staying air flows and reaches the pump, and there is a problem in that the pump causes failure of air entrainment. Meanwhile, since various devices such as a circulation pump are disposed below the hot-water storage tank and the space is not enough, if the liquid-liquid heat exchanger is disposed below the hot-water storage tank, a base which lifts the hot-water storage tank is required. Thereby, the center of gravity of the hot-water storage tank rises, the hot-water storage tank becomes unstable, and there is a problem in that drainage of the hot-water storage tank is difficult. Therefore, the liquid-liquid heat exchanger is disposed on the Side of the hot-water storage tank.